I have a service fabric cluster that hosts some number of identical applications. The application has two main components - a stateless service that hosts web api (it listens on unique port number) and an actor service.
In front of it there is an application gateway instance with multisite listeners to reach proper application instance based on the url. The scale set for the service faberic cluster is set as backend pool for the application gateway.
For each application I have separate http settings with a unique backend port to reach. One of the configuration options for a listener is a health probe that check the web api health, by default on each backend node.
There is no problem when the api is deployed on each node on the backend, but when the api is deployed only on subset of nodes, for the nodes without it the health probe reports this app as unhealthy.
Is there a supported way to configure the application gateway health probe to check health only on a subset of backend nodes. For apps running on a service fabric cluster like in my case it will be strongly desired.
I recommend that you use a reverse proxy on the cluster for this. You can use the built-in reverse proxy, or Traefik for this.
This ensures that all incoming traffic is routed to the services.
It does introduce an additional network hop, so there is a performance impact.
Environment Details: I have an application hosted in two azure environments for two clients. The application contains ASP.NET web API backend and Angular Frontend. Both applications hosted on two web servers (Windows VM). I'm using LB in the first environment (Environment 1) and using AGW in the second environment (Environment 2).
Problem: The issue that I'm having is, environment 1 API request response time is faster than the environment 2. Below is the screenshot of the browser inspect window for the same request.
According to the timing tab, environment 1 has a fast response time than environment 2.
Question: My question is whether this response time difference due to using LB and AGW?
The biggest difference between Azure load balancer and Azure application gateway is that they works at the different layer at OSI Model. Azure Load Balancer is a high-performance, low-latency Layer 4 load-balancing service (inbound and outbound) for all UDP and TCP
protocols. This might make a quick request and response relatively.
Application Gateway provides application delivery controller (ADC) as
a service, offering various Layer 7 load-balancing capabilities. Use
it to optimize web farm productivity by offloading CPU-intensive SSL
termination to the gateway.
Azure Load Balancer is a high-performance, low-latency Layer 4
load-balancing service (inbound and outbound) for all UDP and TCP
protocols. It is built to handle millions of requests per second while
ensuring your solution is highly available. Azure Load Balancer is
zone-redundant, ensuring high availability across Availability Zones.
For more references:
Overview of load-balancing options in Azure
Azure — Difference between Azure Load Balancer and Application Gateway
I have always worked on mobile technologies and now I am stepping into backend systems, more specifically systems design. I keep coming across conflicting statements for the roles of api gateway and load balancer. Googling has only returned the same half a dozen results that mostly focus on the implementations of load balancer or api gateway service provided by some famous service. I will list here all the confusing I am facing, in hope someone can clarify all of them.
Sometimes, i come across that API Gateway is the single point of communication with client devices. On the other hand, some places mention that 'request goes to load balancer, which spreads it across servers equally'. So what is correct? API Gateway receives requests or load balancer?
Other places, when I googled the topic, say that the two are totally different. I've understood that API Gateway does a lot of stuff, like SSL termination, logging, throttling, validation, etc, but it also does load balancing. So API Gateway is a load balancer itself, equipped with other responsibilities?
On the topic, I want to understand if load balancer distribute load among servers of the same cluster or across different data centers or clusters? And what about API Gateway?
What is so specific to api gateway that it is a choice by default for micro-service architecture? Where are API gateways hosted? A DNS resolves domain name to a load balancer or api gateway?
As it might be clear, I am totally confused. In what systems does a load balancer benefit more than API Gateway, if the question is correct.
API Gateway and Load Balancer are 2 different things.
Load Balancer -> Its a software which works at protocol or socket level (eg. tcp, http, or port 3306 etc.) Its job is to balance the incoming traffic by distributing it to the destinations with various logics (eg. Round robin).
I doesn't offer features such as authorisation checks, authentication of requests etc.
Whereas
API Gateway -> Its a managed service provided by various hosting companies to manage API operations to seamlessly scale the API infra.
It takes cares of the access control, response caching, response types, authorisation, authentication, request throttling, data handling, identifying the right destinations based on custom rules, and seamless scaling the backend.
Generally Managed API gateways by default comes with scalable infra, so putting them behind load balancer might not make sense.
About resolving the Domain, most likely always the DNS resolves to the load balancer, which in turn fetches the response from the API gateway service.
DNS -> Load Balancer -> API gateway -> Backend service
Hope I could explain and clear your confusion.
API gateway predominately does API management and provides various other key features such as IAM (Identity and Access Management), Rate limiting, circuit breakers. Hence, it mainly eliminates the need to implement API-specific code for functionalities such as security, caching, throttling, and monitoring for each of the microservice. Microservices typically expose the REST APIs for use in front ends, other microservices and 3rd party apps with help of API gateway.
However, normally, the API Management does not include load balancing function, so it should be used in conjunction with a load balancer to achieve the same.
In system architecture based on Azure, there is Azure Application Gateway which is a load balancer that runs on Layer 7 and provides more features than traditional load balancer ( Layer 4 ) in terms of routing traffic using routing decisions based on additional attributes of HTTP request or content of traffic. This can also be termed as an application load balancer. It shall be used in conjunction by Azure API Management (API gateway). Azure has a Traffic Manager for operating at DNS level which uses DNS to direct client requests to the most appropriate service endpoint based on a traffic-routing method and the health of the endpoints. Traffic manager also uses the rules configured at the DNS level and enables dstribution of the the load over multiple regions and data centers. Within every region or data center, there shall be application gateways coupled with load balancers such that, the application gateways shall help in determining the application server to fetch response from and the load balancer shall help in load balancing.
System overview based on Azure :
Here are few related references:
Azure Application Gateway - https://learn.microsoft.com/en-us/azure/application-gateway/application-gateway-introduction
Azure Load Balancer- https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-overview
Azure Traffic Manager - https://learn.microsoft.com/en-us/azure/traffic-manager/traffic-manager-overview
Scenario Architecture - https://learn.microsoft.com/en-us/azure/traffic-manager/traffic-manager-load-balancing-azure
There are two scenarios to consider here to clarify the confusion. I have clarified this using microservices example as this would make sense there only.
Scenario 1: You have a cluster of API Gateways
User ---> Load Balancer (provided by Cloud Providers like AWS or your own) ---> API Gateway Cluster ---> Service Discovery Agent (like eureka) ---> Microservice A ---> Client Side Load Balancer ---> Microservice B
Scenario 2: You have a single API Gateway
User ---> API Gateway ---> Service Discovery Agent (like Eureka) ---> Microservice A ---> Client Side Load Balancer -> Microservice B
I hope you understand why we required Load Balancer before the API Gateway in Scenario 1, as there we had multiple instances of API gateway also to handle the large traffic and to avoid the burden on the single api gateway since gateway itself can have several tasks to manage as per the requirements, so to distribute the load among them, we have load balancer.
Inside the microservices environment, you may need load balancing concept at multiple places. Like to accept the outside network you will maintain a load balancer provided by Cloud provider like AWS, eureka (Service Discovery) also acts like a load balancer if there are multiple instances of same service are registered with it and at last we also have client side load balancing (each microservice has its own client side load balancer that maintains a local cache) when your microservices are trying to communicate within them just to avoid burden on service discovery agent(eureka) by not checking every time with it the address for the other microservices.
Note: In the flow diagram, please don't confuse the path from API
Gateway --> Service Discovery --> to Microservice as if the Gateway is
forwarding request to Service Discovery that later routes it forward.
Gateway is just checking for the services registry from the Discovery
agents and then routing it to the correct microservice (Not through
the Service Discovery agent)
Load Balancer :
Its main purpose is to distribute by load balancing traffic between multiple back end systems.
We can configure different routes for different back end systems.
We get a static ip address for the load balances end points (usually not available with API gateways)
Can configure health checks (usually not available with API gateways)
In case of cloud providers, usually "Pay for idle as well"
API Gateway :
This as well routes traffic to back end systems based on URL
BUT, its main purpose is targeted towards "API management".
Below are such key features which are usually not available in "Load Balancers",
Can implement rate limiting, bursting limits
Can do request validation and request/response mapping
Usually cloud API gateways allows to export/import cross API platform using swagger spec
Allows caching responses
In case of cloud providers, usually "Pay per use"
DNS is responsible for routing the request to the nearest ip address inside network for a given domain name.
Api gateway is responsible for authentication, finding the correct apis(with or without load balancer) to call and circuit braking, response consolidation.
Load balancer is resposnible for distributing incoming request to different machine having same service deployed on them, on the basis of load or maybe round robin fashion.
So one way of doing it is
DNS TO GATEWAY TO LB
NOTE : LB can be placed before gateway depending upon traffic and use case
I have 2 same Web App and I have added them to application gateway's backed pool in Azure.
I have one domain for the application Gateway and I can bind only one web app to it.
Is there any way to add 2 Web App with the same domain of application gateway?
If not, then any other way to achieve high availability for Web Apps?
I want that if one Web App is not reachable, the traffic should go to other Web App. The Web Apps are not stateless and therefore ruled out the use of Traffic Manager Profile due to lack of Session Persistence.
I have gone through various questions mentioned below on the same topic, but none is related or have satisfactory solution.
- DNS: High Availability with Azure Web Apps + Traffic Manager
- Achieving High Availability using Azure Traffic Manager
- Is it possible that one domain name has multiple corresponding IP addresses?
For App Service, Application Gateway cannot be used for Load balancing Purpose. You can use Application Gateway as WAF. In your scenario, as Thomas stated, AFD would be the best option.
You can leverage the priority option which can be configured while adding App Service to the backend pool to achieve your ask.
You can assign priorities to your different backends when you want to use a primary service backend for all traffic, and provide backups in case the primary or the backup backends are unavailable.
In this case, when the probe to the Primary goes down, then the traffic will be routed to the secondary Web App.
Reference: https://learn.microsoft.com/en-in/azure/frontdoor/front-door-routing-methods
I'm trying to add web app endpoints from the same location, to an azure traffic manager, when I try to do this, it tells me that App Service will use load balancing to do this for me, when we apps are in the same location.
My understanding is that load balancing is for distributing requests between multiple VMs on one web app. The plan was to use out single DNS and allow traffic manager to determine which endpoint to go to using round-robin or failover. How will load balancing know to direct to one of the web apps from this single address?
Azure Web Apps already have built in load balancing between instances within the web app. So for example if you have a web app with 10 instances under the endpoint: tester.azurewebsites.net, Azure load balances appropriately across those instances.
When you bring in traffic manager, that is looking for different endpoints to facilitate between. Incoming requests will be routed based on proximity to endpoints it is managing, load and if the endpoint is available. Traffic Manager takes care of all of those complexities for you.
This allows you to have a single endpoint myapp.azurewebsites.net; which may route to myapp-west.azurewebsites.net and myapp-east.azurewebsites.net. That routing as I indicated is based on proximity, load and availability.
How it actually works is the magic sauce of Azure Traffic Manager. I use it in production and it has been working very well for me. I primarily use it for routing based on proximity, and have yet to experience a failure on a web app to test a production failover reroute.
Hope that helps!